1. Field of the Invention
The present invention relates to a liquid curable resin composition producing cured products with slippery surface, and more particularly, to a liquid curable resin composition suitable for use as a coating material for optical fiber ribbon matrix and the like.
2. Description of Related Art
In the production of optical fibers, a resin coating is provided for protection and reinforcement immediately after spinning molten glass fibers. A known structure of the resin coating consists of a primary coating layer of a flexible resin which is coated on the surface of optical fibers and a secondary coating layer of a rigid resin which is provided over the primary coating layer. A so-called optical fiber ribbon is known in the art in the application of optical fibers provided with resin coating. The optical fiber ribbon is made from several elemental optical fibers, e.g. two four, eight or twelve optical fibers, by arranging these fibers in a plane and fixing them with a binder to produce a ribbon structure with a rectangular cross section. The binder for preparing the optical fiber ribbon from several optical fibers is called a ribbon matrix material. A multiple core ribbon structure consisting of several optical fiber ribbons is also known. The material for binding the optical fiber ribbons is called a bundling material.
The characteristics required for curable resins used as the coating materials for optical fibers include: to be a liquid at ordinary temperature and have a sufficient low viscosity to be excellently coated; to have superior storage stability producing little unevenness in the composition distribution; to provide good productivity at a high curing rate; to have sufficient strength and superior flexibility; to exhibit very little physical change during temperature changes over a wide range; to have superior heat resistance and superior resistance to hydrolysis; to show superior long term reliability with little physical changes over time; to show superior resistance to chemicals such as acids and alkalis; to exhibit low moisture and water absorption; to exhibit superior light resistance; to exhibit high resistance to oils; to produce little hydrogen gas which adversely affects optical fiber characteristics; to produce cured products with slippery surface.
In addition, in the manufacture of optical fiber ribbons and multiple core optical fiber ribbons it is important that the ribbons manufactured are smoothly wound up and the wound ribbons can be smoothly drawn out at a specific rate to smoothly manufacture optical fiber cables in the succeeding step. Conventionally, a lubricant such as silicone oil or a powder such as talc has been applied to the surface of the ribbon to provide slippery surface, whereby smooth wind-up and draw-out operations of the optical fiber ribbons are ensured.
Another method to provide good surface slip characteristics is a method of adding an additive such as silicone oil to the ribbon matrix material or the bundling material. The use of conventional additives, however, impairs the storage stability of the composition, that is, the addition of a large amount of additives causes the liquid composition to be separated into two layers during storage, although the surface slip characteristics of the cured product are improved. If the amount of such an additive to be added is too small, it is necessary to apply a powder such as talc when ribbons are produced, because the cured product does not have sufficient surface slip characteristics, even though the storage stability is excellent.
A ribbon matrix material or a bundling material which can produce optical fiber ribbons without applying a lubricant such as silicone oil or a powder such as talc to the surface of the ribbons is strongly desired. The capability of producing cured product with slippery surface is an important characteristic for the tape material or the bundling material.
In addition, the liquid curable resin composition must not produce liquid-liquid phase separation and must be homogeneous after having been stored for a long period of time, and the cured product must maintain the same characteristics as possessed at the time of production, even when the additive for the improvement of surface property is added.